1. Field of the Invention
The present invention relates to a stereoscopic endoscope which can stereoscopically observe subject parts such as those inside body cavities and, in particular, to an improvement in configuration of an objective optical system disposed at the tip portion of its inserting portion.
2. Description of the Prior Art
Recently prevailing is a surgical technique in which endoscopes are used for observing subject parts within body cavities and performing operations of affected parts within the body cavities. In order to effect accurate diagnosis and alleviate sufferings of patients, the endoscopes have been technically being improved. In particular, in order to carry out more accurate diagnosis within a body cavity, it is useful to obtain depth information within the body cavity. Stereoscopic endoscopes have been known to respond to such a demand.
Known as such a stereoscopic endoscope is the one disclosed in Japanese Unexamined Patent Publication No. 8-122665, for example.
The endoscope objective optical system disposed at the scope tip of the stereoscopic endoscope disclosed in this publication comprises, successively from the object side, a pair of negative lenses disposed in parallel to each other, and a group of concentric positive lenses. As the number of lens sheets at parts which are separated into right and left sides is reduced, error between right and left images is minimized. Accordingly, the right and left images are easily merged with each other, whereby the fatigue of an observer is alleviated. Also, as a parallel negative lens pair is disposed at the leading end of the scope, its positional adjustment is facilitated. Consequently, when assembling the endoscope, an optimal lens position for three-dimensional feel and eccentricity error adjustment of the right and left images can be easily set.